Most Abundant Organism in the Ocean Creates Methane

Methane is about 20 times more powerful as a greenhouse gas than carbon dioxide and it supersaturates the surface waters of the world's oceans. Yet where exactly this methane comes from has long remained a mystery-until now. Scientists have found that some strains of the oceans' most abundant organism, SAR11, can generate methane as a byproduct of breaking down a compound for its phosphorus.

"Anaerobic methane biogenesis was the only process known to produce methane in the oceans and that requires environments with very low levels of oxygen," said Agelicque White, one of the researchers, in a news release. "In the vast central gyres of the Pacific and Atlantic oceans, the surface waters have lots of oxygen from mixing with the atmosphere-and yet they also have lots of methane, hence the term 'marine methane paradox.'"

Previous research has actually shown that adding methylphosphonic acid, or MPn, to seawater produces methane. That's why scientists decided to take a closer look. In the lab, the researchers found that an organism called Trichodesmium could break down MPn and use it as a source of phosphorus. Yet these creatures are rare in the marine environment. That's why researchers examined different SAR11 strains to see if they would consume MPn and cleave off methane.

SAR11 is the smallest free-living cell known to man. It also has the smallest genome of any independent cell. Yet SAR11 dominates life in the oceans and plays a huge role in the carbon cycle on Earth.

"We found that some did produce a methane byproduct, and some didn't," said White. "Just as some humans have a different capacity for breaking down compounds for nutrition than others, so do these organisms. The bottom line is that this shows phosphate-starved bacterioplankton have the capability of producing methane and doing so in oxygen-rich water."

The findings reveal the source of methane in ocean waters. That said, more research is needed before scientists can determine how much they contribute to the amount of methane in the atmosphere and on Earth.